Cyclic Steaming is a method of increasing oil recovery from an oil field where the oil is contained in earth that has low permeability. The low permeability slows or prevents flow of oil thus inhibiting the recovery of oil. Cyclic steaming is a method that greatly increases the permeability of the earth in such a field and at least temporarily increases the oil production from individual wells and the field as a whole. Generally any given well in such an area must be repeatedly steamed as production decreases over time. Typically after a particular steam event a well produces at a high rate for some period of time, but the rate decreases over time until it is no longer producing efficiently and needs to be re-steamed. The rate of decline in production by a given well can vary quite significantly. Also the amount of production to be expected from wells within a particular field can vary radically. It is generally desired to maximize the amount of oil produced in a particular field over time given a finite amount of steam available. Thus given the variability of potential production of individual wells within a field it is important to choose carefully which wells to steam and when to steam them in order to maximize oil produced by the field.
A Patent that describes the Cyclic Steaming process is U.S. Pat. No. 5,085,276 which is herein incorporated by reference in its entirety. Cyclic steaming can be accomplished as follows: The method generally involves the drilling of a wellbore which traverses the low permeability formation. First, a lower interval within the low permeability formation is selected and perforated. Tubing is run into the wellbore, and a thermal packer is set at the upper boundary of the low permeability formation to be produced. Steam is injected into the wellbore through the tubing at sufficient pressure and flow rate to cause the low permeability formation at the first selected lower interval to accept fluid in the case of naturally fractured low permeability formations, or to fracture in other formations such as diatomite. The steam injection is continued until a predetermined quantity of steam has been injected. Following a relatively short “soak” period, the well is allowed to produce back from the first set of perforations. Short steam cycles alternating with production are repeated for the first interval in the wellbore. Next, sand or sand in combination with other material impervious to steam such as cement, or a mechanical isolation device, is placed into the wellbore sufficient to prevent steam from entering the formation through the first set of perforations. A second interval in the low permeability formation is then selected and perforated. Steam is once again flowed from the surface down the wellbore and may enter the formation only through the new second set of perforations due to the impervious sand or other blocking means in the wellbore. After a predetermined amount of steam is flowed into the formation to cause controlled fracturing from the second set of perforations, the steam flow is ceased and after another short soak period of about five days, the well is allowed to produce from the second interval. Again, alternating steam and production cycles of short duration without a significant period in between due to well pump pulling is accomplished. The sequence of perforating, steam fracturing, and cycle steaming and producing the new fractures, followed by sanding back or otherwise isolating, and repeating at an upper interval is repeated until a desired amount of the low permeability formation has been fractured and completed by the controlled technique of the present invention.
When the final set of perforations has been completed, steamed and produced for several cycles, the sand, isolating device or other steam impervious material is circulated out, or drilled through, so as to open all the perforations and place the fractured intervals in fluid communication with the wellbore. Steam from a surface steam generator may then be flowed down the tubing and into the entire set of previously isolated perforations, and after a short cycle of steam followed by a soak period, the well is returned to the production mode. Alternatively, any single or set of fractured intervals may be isolated and selectively re-steamed.
As mentioned above it is desired to maximize the amount of oil produced using Cyclic Steaming, or minimize steam usage or total cost or optimize some other criteria, in a particular field over time given a finite amount of steam available. The method of the present invention provides a means for producing an optimized steaming schedule in order to optimize for selected optimization criteria.